Who has used a P14 action for a custom magnum build?

[tobnpr]

Blown actions often are seen with pieces of brass that had been molten, then froze to the steel. Once high pressure gas is released into the bolt lug recess or the magazine well, it expands rapidly. It blows the receiver ring apart, which allows the barrel to move forward and the bolt to move back, which releases more gas which continues to expand and causes even greater damage.

OK. Sounds logical to me. But...

This scenario seems to assume that there is a pressure overcharge that causes the extreme flow of the brass, it's subsequent failure, release of gas, receiver failure...correct? This wouldn't happen otherwise with factory or other correctly designed loads- without a defect.

In the case of Mobuck's failure though (and other military actions) that fail when there is not an overpressure, what causes the receiver ring failure? Sorry- not trying to beat a dead horse here but still not following...

Are we to assume, that in order for that type of failure to occur-your scenario , or Mobuck's failure, there had to be something else "amiss"- perhaps an already stretched, or otherwise weak or defective casehead, or excessive headspace- that caused the sudden release of gas to blow apart the receiver?

To clarify (and guess I'm being a stupid PITA here), I am still trying to understand the role of the receiver ring, as relates to the overall ability of the action to withstand magnum chambering pressures. IOW, under normal circumstances, what loads are placed on the receiver ring- which would presumably be exceeded by a magnum cartridge for which it wasn't designed?

I inquired with Savage and Remington about using a "standard" magnum action, for a .338 LM. Both told me, the bolts / receivers were not designed for the bolt thrust generated by this cartridge. I get that- a sheared lug..but this is different.

 

[James K]

In actions like the Mauser, the receiver ring contains the locking lug seats. In other words, the bolt locks into the receiver. In actions like the Lee, the bolt locks into the receiver at midpoint, and the receiver ring basically serves only to support the barrel. In the Lee, for example, very high pressure tends to stretch and bend the receiver behind the receiver ring. That allows the bolt to move back, opening a gap between the barrel and the bolt. And that, in turn, allows the case to blow out and destroy the action.

Of course not all blown actions are due to high pressure. The "normal" pressure in most rifle cartridges is more than enough to wreck a rifle and injure the shooter if it is let loose.

In my limited experience (I don't blow up rifles for a living, though some folks at places like Remington do just that), other causes have been flaws in the barrel metal, flaws in the receiver, and receiver material that was not intended for that use (e.g., cast iron). A flaw (occlusion or hidden flaw) aside, the barrel will stand up to about any pressure put on it; it is the strongest component. Shearing of bolt lugs has happened, particularly in the early 20th century when metallurgy was not well understood, but is unknown in modern rifles (many old designs, like the M98 Mauser and M1903 Springfield have "safety lugs" to act as a backup in case of failure of the primary lugs.

Most modern rifles still have a safety lug of some kind, but it is rarely, if ever, called upon, being more for giving the shooter a "warm, fuzzy" than for any real need.

As to Mobucks' failure, I would suggest the following:

- The receiver was already cracked or cracked when the old barrel was removed (a problem with 1917's, especially Eddystones). Such cracks are often not visible to the naked eye.
- The annealing for drilling and tapping was too extensive and perhaps not properly done, leaving that part of the receiver soft or brittle.
- Firing caused the crack to extend to the point that it allowed too much bolt movement. If the receiver ring was soft, each firing would also increase headspace.
- The cone breech of the 1917 could also have played a part by having less casehead support than other rifles, even with a belted case.
- The left side of the receiver was blown back by escaping gas, causing the major damage to the shooter.

The exact cause probably could not be determined without an extensive (and expensive) metallurgical analysis. Since any legal action is unlikely (sue whom?) that kind of research is moot.

Jim

 

[F. Guffey]

- The cone breech of the 1917 could also have played a part by having less case head support than other rifles, even with a belted case.

There is more case head support on the 03 and M1917 than most other rifles. ‘About” the only protrusion of the case head from the cone cut is the case head from the top of the extractor cut to the case head’ expect for that part I have explained 50 times, except when measured from the bottom of the extractor cut to the case head. When measured from the bottom of the extractor cut to the cases head there is .090” case head protrusion. That is .020” less case head protrusion than the Mauser; the Mauser has .110”

Again, who measures the case head thickness? I do; the most thin case heads I have are .200” thick, the thickest I have are .260”.

F. Guffey